A metal rod of length 10 cm has a rectangular cross-section of 1 cm by 1/2 cm. A battery is connected across two opposite faces. The resistance between the faces is:

maximum when connected across the 1 cm x 1/2 cm faces
maximum when connected across the 10 cm x 1 cm faces
maximum when connected across the 10 cm x 1/2 cm faces
the same for all three pairs of faces

Correct answer: maximum when connected across the 1 cm x 1/2 cm faces

Solution

Connecting across the 1 cm x 1/2 cm faces makes the current path 10 cm long with the smallest area, giving maximum resistance.

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